1. Field of the Invention
The invention relates to a power converter and a method for manufacturing the power converter. The invention especially relates to a power converter, in which a plurality of power cards that respectively house semiconductor elements, and a plurality of coolers are laminated, and to a method for manufacturing the power converter.
2. Description of Related Art
A power converter generates a large amount of heat. A switching element, or a semiconductor element for power conversion, which is called a power element, generates a particularly large amount of heat. For example, a power converter that supplies power to an electric vehicle driving motor is provided with a large number of switching elements, and thus generates an especially large amount of heat.
Japanese Patent Application Publication No. 2012-238681 (JP 2012-238681 A), Japanese Patent Application Publication No. 2006-165534 (JP 2006-165534 A), and Japanese Patent Application Publication No. 2012-009568 (JP 2012-009568 A) disclose techniques for aggregating a large number of switching elements having a large amount of heat generation and cooling the switching elements effectively. In the technique disclosed in JP 2012-238681 A, a lamination unit is employed, in which a plurality of power cards housing switching elements, and a plurality of coolers are provided, and the power cards and the coolers are laminated alternately. Each of the flat plate-type power cards is cooled by making the coolers abut on both surfaces of each of the power cards. JP 2012-238681 A discloses that a body of the cooler is aluminum. It is known that this type of cooler is easily manufactured by pressing metal having high thermal conductivity (typically aluminum). The lamination unit is housed in a power converter case while applying pressure on the lamination unit in the laminating direction of the lamination unit in order to improve efficiency of heat transfer from the power card to the cooler. In JP 2012-238681 A, pressure is applied to the lamination unit by inserting a leaf spring between an end surface of the lamination unit and an inner side surface of the case.
In JP 2006-165534 A and JP 2012-009568 A, a lamination unit is disclosed, in which a power card is assembled into a cooler having a resin body inside of which flows refrigerant, and the coolers are laminated. In this lamination unit, unlike the technique described in P 2012-238681 A, refrigerant flows around the power card. Therefore, cooling performance is high.
In Japanese Patent Application Publication No. 2004-180824 (JP 2004-180824 A), an example of a gasket is disclosed.
In the lamination unit described in JP 2012-238681 A, the body of the cooler is manufactured from sheet metal from the viewpoint of ease of forming and thermal conductivity. However, when pressure is applied on the laminating direction on the cooler manufactured from sheet metal, the cooler is deformed greatly, causing a large position error of the power card.
The techniques described in JP 2006-165534 A and JP 2012-009568 A realize high cooling performance without a need for such a cooler described in JP 2012-238681 A by exposing the power card directly to a flow of refrigerant. However, since the power card is directly exposed to a flow of refrigerant, it is difficult to take measures to waterproof the power card.